De Novo CD5⁺ Diffuse Large B-Cell Lymphoma: Biology, Mechanism, and Treatment Advances

Despite its low frequency in all variants of diffuse large B-cell lymphoma (DLBCL), CD5⁺ DLBCL has gradually gained the attention it deserves, the result of its poorer outcomes compared to DLBCL without the CD5 signature. CD5⁺ DLBCL is classified as activated B-cell-like (ABC)/non-germinal-center B-cell-like (GCB) DLBCL with elusive genetic features, and patients are frequently characterized as being older and female, and as having Eastern Cooperative Oncology Group performance status > 1, high International Prognostic Index score, tendency to develop B symptoms, and advanced-stage disease with high central nervous system relapse and bone marrow involvement rate. The mechanism underlying the poor prognosis in CD5⁺ DLBCL has not been fully explored, and we summarize the reported potential mechanisms, including CD5-mediated B-cell receptor (BCR)-dependent and -independent pathways. The former involves the inhibition of BCR signaling, and the latter involves the BCR-independent overexpression of interleukin 10, Bcl-2 (antiapoptotic B-cell leukemia/lymphoma 2), cyclin D2, and CXCR4 (C-X-C motif chemokine receptor 4). The efficacy of traditional regimen R-CHOP (rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone) is currently not satisfied in CD5⁺ DLBCL. Therapies of larger doses, such as R-DA-EPOCH (etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin plus rituximab), R-ACVBP (rituximab plus doxorubicin, cyclophosphamide, vindesine, bleomycin, and prednisone), R-DA-EPOCH plus central nervous system prophylaxis, can improve the overall survival in CD5⁺ DLBCL patients, while allogeneic hematopoietic stem-cell transplantation still remains controversial as a salvage treatment. In addition, some novel drugs, such as lenalidomide, CXCR4 antagonists, Bruton tyrosine kinase inhibitors, Bcl-2 inhibitors, and immunotherapy, have been reported to have encouraging results and may improve the outcomes of these patients. In the present review, we comprehensively summarize the biology, mechanism, and treatment of CD5⁺ DLBCL.